Processing of a peripheral edge of a lens for spectacles, in which the spectacle lens is processed in compliance with the configuration of a lens frame of a spectacle framework, has conventionally been carried out practically in such a manner that a spectacle lens to be processed is profiled on the basis of a template formed by a plain plate having the same configuration as the lens frame. In case of this profiling, the template and the lens to be processed are held in coaxial relation to each other, a follower in contact with the template and a columnar grindstone for cutting the lens are held in coaxial relation to each other, and the lens to be processed is urged against the outer peripheral surface of the grindstone to grind the lens to be processed. This profiling requires high skill in order to carry out accurate lens processing. In addition, since it is not necessarily possible for the profiling to obtain highly accurate spectacle lenses, it has been required to rectify the lens by means of manual grinding after the profiling.
Moreover, in recent years, a processing machine for peripheral edges of spectacle lens by means of a numerically-controlled system has been developed (refer to, for example, Japanese Patent Application Laid-Open No. 61-267732). In this case, the processing machine takes not only the data on the configuration of the lens template, but also data on the configuration of the lens frame of the spectacle framework directly in which these data are converted into grinding data for the lens. This processing machine comprises spectacle-framework holding means, support means supporting the spectacle-framework holding means for movement in a predetermined plane, and measuring means. This measuring means is composed of a sensor arm rotatable about an axis normal to the aforesaid plane, and a sensor movable along the sensor arm, in which the configuration of the lens frame of the spectacle framework or the configuration of the template is measured, in the form of radial data, on the basis of rotational angle of the sensor arm and an amount of movement of the sensor.
In the numerically-controlled type lens processing machine, the measuring means is complicated in mechanism, and a manner of operation is also complicated and is time-consuming. This is because it is required to obtain the geometric center of the lens frame on the basis of first data on the lens-frame configuration from the measuring means and, subsequently, again to bring the center of rotation of the sensor arm into coincidence with the geometric center, thereby obtaining a measurement value of the lens-frame configuration.
Furthermore, in cases of both the above-described arrangements, the lens is abutted against the grindstone under the own weight of the lens holder. No particular problem arises for such uniform natural fall load, if the lens is hard and thick in wall thickness like glass lens. However, if the lens is relatively soft and thin like a plastic lens, there occurs cracking of the lens, reduction in grinding accuracy, and the like.
It is therefore an object of the invention to provide a method of and an apparatus for processing a peripheral edge of a spectacle lens, capable of directly carrying out processing of the peripheral edge of the spectacle lens on the basis of data on measurement of a configuration of a lens frame of a spectacle framework.
Further, it is an object of the invention to provide a method of and an apparatus for processing a peripheral edge of a spectacle lens, in which measuring means is relatively simple in structure and it is possible to accurately measure the configuration of the lens frame.
Moreover, it is an object of the invention to provide a method of and an apparatus for processing a peripheral edge of a spectacle lens, capable of varying cutting pressure acting upon the lens depending upon the material, the wall thickness and the like of the lens.